1. Field of the Invention
This invention relates to fabrics for reinforcing stucco layers on walls, particularly on rigid foam insulation boards. Such fabrics are made in the form of a grid with openings between the strands. The fabrics are then coated with a resin which does not close the openings. The open grid fabric of this invention is made from certain selected rovings by weft insertion warp knitting, by certain weaving techniques, or by securing a laid, nonwoven grid together by adhesive alone. The present invention also relates to methods of making such reinforcement fabric, to methods for reinforcing such wall systems, and to wall segments that utilize the novel reinforcement disclosed herein.
2. Description of the Related Art
A popular method of constructing walls comprises a wall system in which a rigid plastic foam insulation board is bonded to a concrete or other wall. The insulation board is covered with a layer of reinforcement fabric, and thereafter a stucco or stucco-like material is applied to the fabric and board to embed and cover the fabric. The fabric may be initially attached to the insulation board mechanically with staples, nails, screws or the like. Alternatively, the fabric may be attached to the insulation board by means of an adhesive spread onto the insulation board. The stucco-like material, which is often referred to as a base coat, is typically a polymer modified cement containing, for example, Portland cement and an acrylic or other polymer or copolymer. During fabrication of the wall system, the fabric is buried in the stucco-like material. Openings in the fabric permit the stucco-like material to be pushed through the fabric and contact the insulation board. The stucco-like layer with reinforcement fabric buried in it may range from about 1/16 inch to 1/4 inch thick. Finally, a finishing coat is usually placed on top of the base coat to provide, among other things, better appearance and perhaps better weather resistance.
In such wall systems, a wall segment may be prepared either in situ on the outside of a building or in the form of prefabricated panels.
A primary purpose of the reinforcement fabric in these systems to provide the wall with impact resistance for durability. The reinforcement fabric must, however, have several performance and application requirements: (1) the reinforcement should be economical; (2) the reinforcement should be as light in weight as possible; (3) the reinforcement should greatly increase the impact resistance of the wall system; (4) the reinforcement should provide some resistance to shrinkage cracking, which occasionally occurs in, for example, polymer modified cement stucco materials; (5) the fabric should confer vibration resistance to the wall; (6) performance of the reinforcement should not deteriorate significantly over an extended period; (7) for purposes of installation, the reinforcement should have applied thereto a resin which gives the reinforcement a "hand" or "limpness" to conform to changes in the profile of the wall (for example, at corners or bends), but the reinforcement should not be so limp as to "bunch up" or fold during trowelling of stucco thereon, nor should resin on the reinforcement be so soft that the fabric sticks to itself on a roll before installation (a phenomenon known as "blocking"); and (8) the reinforcement must have enough integrity to prevent distortion or dislodging of the yarns during handling and covering with stucco or stucco-like material. Numbers (7) and (8) refer to the pliability and body characteristics of the fabric that are important during application of the fabric and the stucco-like layer to the board and may be referred to as "application attributes."
Typically in the prior art, fabrics made of oil/starch sized yarns and coated with resins have been used as reinforcements in wall systems, but these fabrics have been woven fabrics, manufactured using conventional weaves, such as a plain weave with looper yarns, and conventional leno and hurl leno weaves. Nonwoven scrims of the kind held together solely by adhesive resin have also been used, but to a lesser extent. Leno weaving is a process in which warp or machine-direction yarns are arranged in pairs and the fill yarns (also referred to as weft or cross-machine yarns) extend across the fabric as in a plain weave, but the warp yarns are alternately twisted in a left hand and right hand direction, crossing before each weft yarn is inserted. FIGS. 1 and 2, in which the warp yarns are vertical, show examples of conventional leno weaves. FIG. 1 shows a regular leno weave, and FIG. 2 shows a hurl leno weave. FIG. 3 shows an example of a plain weave with looper yarns. As can be seen in the figures, these weaves provide an open grid, but in these weaves the warp strands are of equal yield (weight, volume, thickness, etc.) and tend to pinch the weft strands by a scissor action. We have found this can reduce penetration of the resin coating and decrease the impact resistance of the fabric. Also, such fabrics can become kinked or crimped during application.
Conventional reinforcements are generally referred to as "scrim" in U.S. Pat. No. 4,522,004, "woven glass fiber scrim" in U.S. Pat. No. 4,525,970, or "open-weave mesh" in U.S. Pat. No. 4,578,915.
Prior art wall system reinforcements using fabrics of the kinds shown in FIGS. 1 to 3 have typically been composed of fiberglass. Fiberglass yarn with oil/starch sizings have been used in the warp direction, while yarns with oil/starch sizing or rovings direct-sized with a silane sizing have been used for the fill or weft. The individual warp yarns are generally about one half the weight of the weft yarn or roving. In this way, the strength of each pair of warp yarns is comparable to that of the individual weft yarns or rovings.
Sizings, in general, refer to film forming resinous polymers that are applied to strands to provide additional smoothness, abrasion resistance and other properties. Conventional sizings include lubricants such as starch, wax, lacquer, oil and/or anti-static chemicals such as quaternized amines. Oil/starch sizings have been preferred for fiberglass for reinforcements for wall systems because they are inexpensive, they provide the best lubrication and properties for weaving, and they may be removed by rinsing or burning if need be. Silane sizings, however, are sometimes used on fiberglass yarns to be incorporated into fiberglass reinforced plastics (FRP's). While silane sizings are not as good for weaving and processing, unlike starch and other conventional sizings they are compatible with the plastics used in FRP's. (Fabrics for FRP's made from such silane-sized rovings, however, are tightly woven or closely knit fabrics, and they are not pre-coated with polymer resins to form a coated, semi-rigid, open grid, as in the present invention.) Silane sizings may be applied directly to the roving before weaving or similar processing. Rovings made in this way may be referred to as direct-sized with a silane sizing. Generally, the exact compositions of "silane sizings" are kept secret by fiberglass manufacturers. Silane sizings are understood, however, to contain mainly silanes, since starches, oils and waxes may be incompatible with FRP plastics. Some silane sizings are a combination of a silane sizing and another sizing.
We have discovered, however, that it is possible to achieve results comparable to or better than those achieved by the prior art but using significantly less weight of yarn in the fabric, with consequent economies and reduced weight in the final wall. Alternatively, with the reinforcement of our invention, at comparable weight and cost, one is able to achieve significantly greater strength, durability and impact resistance.
Accordingly, it is one object of the present invention to produce an improved open grid fabric for reinforcing wall systems.
It is another object to reinforce a wall system and to provide a wall segment that utilizes the improved open grid fabric of the present invention.
These and other objects that will become apparent may be better understood by the detailed description provided below.